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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The sources of the suspended particulate matter derived from the summer mixing of Columbia River and ocean waters are river-borne particles, phytoplankton growing in the ocean near the river, and resuspended particles. The Columbia River contributes most of the particulate (>= 0.45µ) matter (8 to 40 mg/l) which consists of lithogenous particles (85-95 percent) and biogenous particles--primarily freshwater phytoplankton with lesser amounts of detritus. Biogenous matter, primarily phytoplankton and detritus (<= 3 mg/l), constitutes the bulk of the particles found in the ocean. Resuspended particles, mainly lithogenous, are contributed locally into the water column near the river mouth by strong tidal and hydraulic currents.
Positive vertical gradients in particle concentrations are maintained in the low-salinity surface layers near the river mouth by vertical water movements (>= 1 m/day) and by the relatively greater turbulence of the low-salinity surface layers. The upward component of the water movements is sufficient to retain lithogenous matter (< 4µ) and most biogenous matter in the surface layers while transported seaward (103 to 104 m/day). Concentrations and modal particle diameters (10 to 30µ) of river-borne lithogenous particles, which differ with the rate of river discharge, decrease seaward by progressive mixing with ocean waters with less suspended matter (<= 1 mg/1) and by settling of the (> 4µ) suspended load.
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